Polybutadieneimine and process for preparation thereof

ABSTRACT

A NOVEL COMPOUND, POLYBUTADIENEIMINE, SERVES AS A CROSSLINKING AGENT OR CHAIN-EXTENDING AGENT FORCARBOXYLTERMINATED POLYBUTADIENE PREPOLYMER OR HYDROGENATED CARBOXYL-TERMINATED POLYBUTADIENE PREPOLYMER. THE CROSSLINKED PREPOLYMER IS USED IN CONJUNCTION WITH ALUMINUM AS THE METAL FUEL, AMMONIUM PERCHLORATE AS THE INORGANIC OXIDIZER, AND OTHER ADDITIVES TO FORM A HIGH TEMPERATURERESISTANT PROPELLANT. THE CHAIN-EXTENDED PREPOLYMER IS USED IN ALIKE MANNER WITH THE SPECIFIED POPELLANT INGREDIENTS.

United States Patent 3,734,895 POLYBUTADIENEIMINE AND PROCESS FOR PREPARATION THEREOF David C. Sayles, Huntsville, Ala., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Original application Dec. 5, 1969, Ser. No. 885,394. Divided and this application Aug. 31, 1971, Ser. No. 176,724

Int. Cl. C08d 5/02, 5/04 US. Cl. 260--77.5 R 5 Claims ABSTRACT OF THE DISCLOSURE A novel compound, polybutadieneimine, serves as a crosslinking agent or chain-extending agent for carboxylterminated polybutadiene prepolymer or hydrogenated carboxyl-terminated polybutadiene prepolymer. The crosslinked prepolymer is used in conjunction with aluminum as the metal fuel, ammonium perchlorate as the inorganic oxidizer, and other additives to form a high temperatureresistant propellant. The chain-extended prepolymer is used in a like manner with the specified propellant ingredients.

This is a division of application Ser. No. 885,394, filed Dec. 5, 1969'.

BACKGROUND OF THE INVENTION The prior art has employed polybutadiene for use in combination with the tri(aziridinyl)phosphine oxide and sulfide which compounds are depicted by the illustration as follows:

(LB or wherein X is selected from the group consisting of oxygen and sulfur, P is phosphorous, R, and R are radicals containing up to a total of 20 carbon atoms selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, alkaryl, and aralkyl radicals and R, and R can be the same or unlike.

US. Pat. 3,087,844 issued to P. S. Hudson et al. on Apr. 30, 1963 is concerned with solid composite propellants and the curing of the same with aziridinyl curing agents. Hudson et al. teach that certain polymers (e.g., conjugated dienes containing from 4 to 12 carbon atoms and preferably 4 to 8 carbon atoms such as 1,3-butadiene, isoprene, and the like, and in addition, conjugated dienes containing reactive substituents along the chain, such as for example, halogenated dienes) are admixed with a phosphine compound, tris(aziridinyDphosphine oxide or sulfide, and an inorganic oxidizing salt. After mixing the mixture is suitably increased in temperature so that reaction occurs between the polymer and the phosphine compound to yield a solid propellant structure.

The exact chemistry of the prior art and currently employed processes of the type set forth are not completely understood. However, those skilled in the art recognize that certain competing reactions are encountered when aziridinyl compounds, such as, tris(methylaziridinyl)phosphine oxide and/ or sulfide, are used to crosslink carboxylated polybutadiene prepolymers. When the reaction occurs in admixture, the competing reactions are more 3,734,895 Patented May 22, 1973 numerous because of the presence of other propellant ingredients. The competing reactions may cause excessive number of sites to be formed which can undergo oxidation reactions. It is necessary in a high temperature-resistant propellant that the ingredients be bound with a binder having the necessary crosslink sites to impart strength. However, sites which are not involved in crosslinking, but which may undergo oxidation to produce a reduction in the mechanical properties of the propellant are undesirable sites. 1

The object of this invention is to provide a novel crosslinking agent which is closely related to the binder material structurally and which will undergo ready reaction with the binder material, and impart high temperature-resistant characteristics to the propellant system.

Another object of this invention is to provide a modified polybutadiene crosslinking agent which can be selectively absorbed on the surface of an oxidizer employed in a propellant composition to provide a protective coating and reduce incompatibility of the oxidizer with the other propellant ingredients.

SUMMARY OF THE INVENTION Polybutadiene is changed to an aziridinyl compound (polybutadieneimine) by a series of reactions including: (1) reacting polybutadiene with equimolar quantities of a haloisocyanate in an ethereal solution to form a polybutadiene haloisocyanate; (2) converting the polybutadiene haloisocyanate thus formed by heating gently (e.g., 180 F.) with an appropriate alcohol using sodium or lithium alkoxide as catalyst to form the halocarbamate of the polybntadiene; (3) refluxing the halocarbamate with 1.5 normal sodium hydroxide in methanol to form the polybutadieneimine.

The polybutadieneimine may be recovered by solvent extraction using an inert organic solvent (e.g., diethyl ether, ethyl acetate or the like) followed by solvent removal after which the polybutadieneimine is ready for use.

The polybutadieneimine is used to crosslink carboxylated polybutadiene in a propellant composition to produce a high temperature-resistant propellant. The propellant composition is comprised of polybutadieneimine, aluminum powder, ammonium perchlorate, carboxyl-terminated polybutadiene, ferrocene, dibutyl Carbitol formal, and optional additives, lecithin, etc.

When two moles a haloisocyanate are used for each mole of polybutadiene, a chain-extending agent is pro duced since two aziridinyl functional groups per molecule of polybutadiene are introduced. The chain-extending agent may be used in curing a propellant to achieve desired physical properties. An illustration of the chain-extending function of polybutadieneimine is set forth later herein.

An added feature of polybutadieneirnine is derived when mixed with ammonium perchlorate of the propellant mix. The modified butadiene appears to be selectively absorbed on the surface of ammonium perchlorate. When caused to undergo homopolymerization through the unsaturated linkages, the polybutadieneimine provides an encapsulated protective coating to reduce the incompatibility of the ammonium perchlorate with the other ingredients of the propellant.

DESCRIPTION OF THE PREFERRED EMBODIMENT S An etheral solution of iodine isocyanate can be prepared from the reaction of iodine with silver isocyanate in ether.

3 4 When the reaction is carried out in the presence of polyconditions. When a fiuoroor a chloro-isocyanate is used, butadiene the iodine isocyanate thus formed reacts rapidly the reaction proceeds at a much lower rate unless conwith polybutadiene. The course of reaction can be folsiderably higher temperatures (e.g., in range of about lowed easily since the paling of the brown iodine color 210 F. to 280 F.) are used. The suggested temperature indicates gradual depletion of the reactant, iodine iso- 5 ranges are indicative of the reaction conditions required cyanate. for the respective halogen systems. A pressurized system Reaction (1), wherein the isocyanate group is introduced generally would be required for use in the higher teminto the butadiene, is illustrated as follows: perature ranges. The employment of a pressurized system The structure, results in greater complexities where components of higher volatilities are involved. Such complexities relate to solvent recovery, heat exchange, and require more elaborate represents a monomeric unit of polymerized 1,3-butaproduction facilities, in general, than would otherwise diene. be required. i (1) The molar ratio of the reactant, polybutadiene, to th reactant, the selected haloisocyanate, may range from a INCO ratio of about 1/1 to about 1/4. The preferred range for producing a crosslinking agent and an encapsulation agent OCN I for the ammonium perchlorate being l/ 1. Encapsulation j occurs when the compound, polybutadieneimine, homopolymerizes through the unsaturated linkages of the specified compound. The use of a molar ratio of 1 polybuta- (Where X18 umts) diene to 2 of the selected haloisocyanate is preferred when The product of reacuon (1) reacted wlth an a chain-extended product is intended to be produced.

cohol, represented by ROH (wherein R=lower alkyls), Example I, below, sets forth a control propellant and 2.

yields polybutadiene iodocarbamate depicted as follows: novel propellant composition of the invention in which (2) 02 I polybutadienimine (aziridinylpolybutadiene) is employed m v as a crosslinking agent with a carboxyl-terminated polybutadiene prepolymer to produce a high temperature-resistant binder. Because of the unique characteristics of the When Product is refluxed with normal q aziridinylpolybutadiene, the epoxy resin or tris(methyl- 0118 Sodium hydroxide in methanol, the Product p y aziridinyl) phosphine oxide curing agent normally used as dieneimine is produced which is depicted as f0110WS2 the curing agent or crosslinking agent is not included in (a) H the propellant composition. Also, the amount of the car- N boxyl-terminated polybutadiene prepolymer used in the W preparation of the propellant can be reduced because the L novel compound, polybutadieneimine (aziridinylpolybuta- Structure (3) is useful as a crosslinking agent which is g g contains polybutadiene groups comparable to the 1n er. Illustrated by lnustratlon (5) below- When a tri-(aziridinyl) phosphine oxide or a tripreceding equatiorrsdepict the Series of reactions (aziridinyl) phosphine sulfide is replaced by aziridinylwl'lel'eln equlmolal' quantltlffs of reactants are used- Y polybutadiene, a distinct advantage is obtained. The addiuslng moles of 1 'f Y for each mole of tional and undesirable reaction sites due to the phosphine polybutadiene, two aziridinyl funct1onal groups per moleoxide and/or h hi lfide ti of the pertinent cule are introduced. The resulting structure is illustrated compounds undergo various Side reactions, and these do as follows: not occur when aziridinylpolybutadiene is used in place H H of the tris(aziridinyl)phosphine oxide or the tris(aziri- N dinyl)phosphine sulfide. In addition, because of the stereo /WA chemical interference effects, the aziridinylpolybutadiene is less susceptible to other competing reactions which are encountered when the aziridinyl phosphine oxide or phos- Structure (4) is useful as a chain-extending curing agent phine sulfides are used for crosslinking polybutadiene prewhich is illustrated by illustration (6) below. polymers.

The polybutadieneimine, structure (3), is reacted with The autoignition temperature is compared for the concarboxyl-terminated polybutadiene to provide a crosslinktrol and the novel propellant, and the results are set ing function, illustrated as follows: forth under Example I. The results indicate that the novel H030 MIR-c0 11 strugture L .1: product r W H020 L J 00 NH L J:

When structure (4) product is substituted for structure propellant containing the aziridinylpolybutadiene is far (3) product in reaction (5), a reaction product useful as more resistant to heat than the control propellant which a chain-extending curing agent is formed. The chain-exdoes not contain the specified compound. The increased tending function is illustrated as follows: resistance to heat wherein the time for autoignition of the The haloisocyanate employed may be selected from the 7 novel propellant is prolonged may be due to combinaisocyanates containing iodine, bromine, chlorine, or fluotion of contributing factors. Such factors may be related rine. A bromoor iodo-isocyanate is preferred since the to the encapsulations of the ammonium perchlorate oxreaction with butadiene may be accomplished under less idizer and minimization of reaction sites within the propelharsh conditions (e.g., at lower temperature in range of lent binder systems whereby decomposition prior to auto- F. to F.) and under near atmospheric pressure 75 ignition is lessened.

Polybutadieneimine is used in amounts from about to about percent by weight of the propellant composition. The ranges of the other propellant ingredients, in percent by weight of the propellant composition, are as follows: NH ClO 64-72, carboxyl-terminated polybutadiene prepolymer 5-15, aluminum 1020, dibutyl Carbitol formal 1-3, and ferrocene 0.5-2.

The control propellant and novel propellant were each mixed, cast, and cured in a like manner by techniques known in the art.

A typical procedure for mixing the propellants is to blend a portion of the ammonium perchlorate oxidizer in the polybutadiene binder to produce a paste. Next, the.

ballastic modifiers and additives (e.g., ferrocene, dibutyl Carbitol formal, iron linoleate, etc.) are added to the paste at 140 F. followed by the addition of the aluminum and the remainder of the ammonium perchlorate. The remainder of the ammonium perchlorate and aluminum are added slowly in increments with good mixing between additions in a vertical mixer under reduced pressure. Finally, the curing agents, crosslinking agents, chain-extending agent, and any other optional additives are added to the propellant which is given an additional 1 hour mix under reduced pressure at 140 F. The propellant is cast into a suitable mold and cured at 140 F. for about 24 hours. The cured propellants are tested to determine properties of heat resistance as noted under Example I above.

The aziridinylpolybrutadiene of this invention may be used to replace the curing agent such as the epoxy resin illustrated hereinabove, the phosphine oxide compound or the phosphine sulfide compound noted herein, and a portion of the carboxyl-terminated polybutadiene prepolymer. The quantity of aziridinylpolybutadiene used in propellants may vary from about 5 to about 10 weight percent of the total propellant weight. The quantity employed depends on the requirement such requirement being related to the physical strengths, specific impulse, burning rates etc. needed in the finished propellant. An improvement in the propellant binder is significant relative to the properties required for resistance to high temperature exposure. Since propellants may be subjected to wide high ranges of temperatures, the ability to withstand a high temperature for a longer period of time without autoignition provides a significant safety factor. Also, since reactive sites not required for crosslinking are minimized or absent altogether in the novel propellant hinder, the stability of the novel propellant when stored or used will be far greater than the stability of a propellant which has excessive reactive sites within the propellant binder. The excessive reactive sites could easily result in decomposition in the propellant matrix. Any decomposition within a propellant matrix would be detrimental to the expected results when the partially decomposed propellant charge is used in a missile or other structure having high demands for reproducibility in performance.

I claim:

1. Polybutadieneimine prepared by the process steps of reacting polybutadiene and a haloisocyanate in a molar ratio of polybutadiene of about 1 to a molar ratio of haloisocyanate which can vary from about 4 to about 1 in an etheral solution to form a polybutadiene haloisocyanate; converting the polybutadiene haloisocyanate thus formed by heating in the range of F.280 F. with an alkyl alcohol and in the presence of a catalyst selected from sodium and lithium alkoxide to form the halocarbamate of polybutadiene; refluxing said halocarbamate of polybutadiene in a methanol solution of sodium hydroxide to form polybutadieneimine; and recovering the polybutadieneimine thus formed.

2. The polybutadieneimine prepared by the process of claim 1 and wherein said haloisocyanate is iodoisocyanate and said molar ratio with polybutadiene is 1/ 1.

3. The polybutadieneimine prepared by the process of claim 1 and wherein said haloisocyanate is iodoisocyanate and said molar ratio with polybutadiene is 2/ l.

4. The polybutadieneimine prepared by the process of claim 1 and wherein said haloisocyanate is bromoisocyanate and said molar ratio with polybutadiene is 1/1.

5. The polybutadiene prepared by the process of claim 1 and wherein said ha'loisocyanate is bromoisocyanate and said molar ratio with polybutadiene is 2/1.

References Cited UNITED STATES PATENTS 3,417,059 12/1968 Holfman 26094.7 N X FOREIGN PATENTS 1,225,857 9/ 1966 Germany 26094.7 N X JOSEPH L. SCHOFER, Primary Examiner W. F. HAMROC-K, Assistant Examiner US. Cl. X.R.

260680 B, 2 EN, 94.7 N 

